The invention relates to improvements in methods of and in apparatus for ascertaining one or more characteristics of certain substances, such as tobacco. More particularly, the invention relates to improvements in methods of and in apparatus for ascertaining one or more characteristics (such as the mass per unit length and/or the moisture content) of mass flows of particulate materials, such as fragments of tobacco leaf laminae and/or other smokable substances.
It is already known to ascertain certain characteristics of mass flows of tobacco particles by evaluating the extent of detuning, due to the presence of such substances, of a high-frequency resonator which receives microwaves from a suitable generator and transmits high-frequency signals to a suitable evaluating circuit. The extent of shift of the resonance frequency and damping of such high-frequency signals (in comparison with output signals which are transmitted in the absence of mass flows within the range of the high-frequency resonator) is indicative of the characteristic(s) of the material of the mass flow.
The making of smokers"" products, such as plain or filter cigarettes, normally involves a testing of the mass flow of tobacco particles which are to form the rod-like fillers of such products. As a rule, the testing involves a determination of the mass of tobacco per unit length of the mass flow and/or the moisture content of the particles in the mass flow and/or the dielectric constant of tobacco (as used herein, the term xe2x80x9ctobaccoxe2x80x9d is intended to embrace natural, reconstituted and artificial (substitute) tobacco). An accurate determination of the mass per unit length and of the moisture content is particularly important in connection with the making of cigarettes or other rod-shaped smokers"" products (hereinafter referred to as cigarettes for short). For example, once the percentages of dry ingredients and moisture in a mass flow of tobacco particles are known, one can accurately determine the overall mass of the tested substance by simple addition of the signals denoting the dry mass and the moisture content. The situation is similar in connection with the processing of certain other substances such as foodstuffs, chemicals, textile materials, paper and many others.
German patent No. 40 04 119 discloses the determination of the moisture content of substances in a cavity resonator which is connected to a microwave generator. The patented apparatus resorts to a calibration curve to ascertain the resonance frequency and the half intensity width of the resonance line.
An object of the invention is to provide a novel and improved method of rapidly and accurately ascertaining one or more characteristics of various substances, such as fragments of tobacco in a mass flow of tobacco particles in a production line for the making of rod-shaped smokers"" products.
Another object of the invention is to provide a method which can be resorted to for rapid and accurate determination of various ingredients (such as dry mass and/or wet mass) in mass flows of particulate materials of the type being utilized in the tobacco processing, textile, paper making, chemical, food processing and other industries.
A further object of the invention is to provide method of ascertaining one or more characteristics of mass flow of filter material for tobacco smoke.
An additional object of the invention is to provide method of rapidly and accurately ascertaining one or more characteristics (such as the percentages of solid and liquid ingredients, the total mass and/or the dielectric constant) of a rapidly advancing stream or flow of tobacco or filter material in a cigarette making machine.
Still another object of the invention is to provide a method of in line determination of one or more characteristics of smokable materials, filter materials for tobacco smoke and/or other materials which are being conveyed in the form of mass flows or streams or rods or fillers in various plants of the tobacco processing industry.
A further object of the invention is to provide a novel and improved apparatus for the practice of the above outlined method.
Another object of the invention is to provide a machine or production line which embodies one or more apparatus for the practice of the above outlined method.
An additional object of the invention is to provide the apparatus with novel and improved means for transmitting signals to a resonator arrangement of the above outlined apparatus.
Still another object of the invention is to provide the apparatus with novel and improved means for processing signals being transmitted by the resonator arrangement of the above outlined apparatus.
A further object of the invention is to provide an apparatus which can be utilized with advantage in modern high-speed production lines for the mass-manufacture of plain or filter cigarettes, cigars, cigarillos, cheroots and/or other rod-shaped products of the tobacco processing industry.
Another object of the invention is to provide an apparatus which can be designed to accurately and rapidly ascertain one or more characteristics various substances, such as the dry mass, the moisture content, the total mass and/or the dielectric constant of tobacco particles or filter material for tobacco smoke, in cigarette makers, filter rod makers or other types of production lines.
One feature of the present invention resides in the provision of a method of ascertaining at least one characteristic of a substance by resorting to a high-frequency resonator arrangement which is detuned in the presence of the substance. The method comprises the steps of supplying or transmitting to an input of the resonator arrangement microwaves having at least two different frequencies whereby an output of the resonator arrangement respectively furnishes or transmits first and second curves of high-frequency output signals in the presence and absence of a substance at the resonator arrangement. Such curves have different amplitudes, and the method further comprises the step of evaluating the output signals including comparing the curves to ascertain shifts of resonance frequencies of the output signals due to the presence of a substance at the resonator arrangement and comparing the amplitudes of the curves to ascertain damping of output signals due to the presence of a substance at the resonator arrangement.
The supplying step can include continuously transmitting to the input of the resonator arrangement microwaves having at least two different frequencies.
The method can further comprise the step of periodically varying the frequencies of microwaves which are being transmitted to the input of the resonator arrangement. This varying step can include repeatedly shifting between higher and lower frequency values. Such varying step can also include repeatedly and continuously wobbling between higher-frequency and lower-frequency values. The frequencies of the microwaves can be allocated to a sloping flank of a curve of high-frequency output signals. The wobbling step can involve substantially sinusoidally wobbling the frequencies of the microwaves between threshold values with relatively small frequency changes or differences. The output signals can have d-c fractions and substantially sinusoidally varying a-c fractions. The evaluating step of such method can comprise transmitting the d-c fractions and the a-c fractions to discrete calculating or computing stages, polynomially computing the fractions in the respective stages with constants to thus generate partial signals, and adding or summing the partial signals. Such evaluating step can further comprise ascertaining the constants by parameterization on the basis of reference values of the substance; such reference values can includexe2x80x94as a function of the at least one characteristic to be ascertained in accordance with the novel methodxe2x80x94at least one of the density/mass, moisture content and dielectric constant of the substance being tested.
The aforementioned threshold values can be at least substantially symmetrical with reference to an inversion point of a downwardly sloping flank of a curve.
The at least two different frequencies of microwave signals can be symmetrical with reference to a resonance frequency which is not influenced by the substance being tested, and the at least two different frequencies can be allocated to downwardly sloping flanks of a resonance curve.
The method can further comprise the step of generating the microwaves, and such step can include substantially sinusoidally modulating the amplitude of a microwave oscillation at a relatively low frequency. The modulating step can include maintaining the basic frequencies of the developing frequency bands at a downwardly sloping flank of the curve, preferably or particularly at an inversion point of such flank.
The supplying step can also include transmitting to the input of the resonator arrangement microwaves at two modulation-established frequencies, and the evaluating step of such method can comprise scaling down the microwave frequencies and selectively filtering those frequency ranges which influence the shifts of resonance frequencies and the damping of the output signals.
The substance can consist of or it can contain tobacco, and the at least one characteristic to be ascertained is or can be the mass/density of tobacco.
The substance to be tested can be tobacco in a tobacco particle flow, and the at least one characteristic to be tested can be the moisture content/mass of tobacco. The substance to be tested can contain or can constitute tobacco in a flow of shredded and/or otherwise comminuted (cut) tobacco particles, and the at least one characteristic to be ascertained can be the dielectric constant of cut or comminuted or shredded tobacco.
Another feature of the invention resides in the provision of an apparatus for ascertaining at least one characteristic of a substance (e.g., tobacco). The apparatus comprises a resonator arrangement, and means for supplying to an input of the resonator arrangement microwave signals at least at two different frequencies. The resonator arrangement has output means for the transmission of first and second high-frequency signals which are respectively generated in the presence and in the absence of a substance to be tested at the resonator arrangement, and the apparatus further comprises means for evaluating the first high-frequency signals. The evaluating means comprises means for comparing first and second resonance curves having different amplitudes and respectively denoting the first and second high-frequency signals to thus ascertain shifts of resonance frequency attributable to the presence of a substance to be tested at the resonator arrangement, and means for comparing the amplitudes of the first and second resonance curves to thus ascertain the damping of such amplitudes by a substance to be tested.
The means for supplying microwave signals can include at least one microwave generator which is designed to uninterruptedly transmit to the input of the resonator arrangement microwave signals at the at least two different frequencies. The generator can include means for periodically altering the frequency of the microwave signals.
The means for supplying microwave signals can be designed in such a way that it comprises a microwave generator which is connected to the input of the resonator arrangement and a frequency regulator which is connected with the microwave generator to periodically vary the frequency of signals from the microwave generator between higher and lower values.
Alternatively, the means for supplying microwave signals can comprise a microwave generator which is connected to the input of the resonator arrangement and a frequency regulator which is connected with the generator to continuously and regularly vary the frequency of signals from the generator between higher and lower values.
The at least two different frequencies can be symmetrical to each other with reference to a resonance frequency of the second curve and are located at downwardly sloping flanks of the second curve.
It is also possible to design the means for supplying microwave signals in such a way that it comprises a microwave generator connected to the input of the resonator arrangement and a frequency regulator connected with the generator to continuously and regularly vary the frequency of signals from the generator between higher and lower values. The microwave signals are allocated to downwardly sloping flanks of at least one of the curves. The frequency regulator can be arranged to substantially sinusoidally vary the frequency of signals from the microwave generator. The comparing means of the evaluating means can comprise means for ascertaining d-c and a-c fractions of the first high-frequency signals.
The means for supplying microwave signals can include means for transmitting to the input of the resonator arrangement microwaves at frequencies having upper and lower threshold values and continuously wobbling between such values. The threshold values are at least substantially symmetrical to each other with reference to an inversion point of a downwardly sloping flank of a resonance curve.
The evaluating means can comprise calculating or computing circuits or stages which respectively receive d-c fractions and a-c fractions of the high-frequency signals and include means for polynomially computing or calculating the fractions with constants to thus generate partial signals, and means for summing or adding such partial signals. Such evaluating means can further comprise means for ascertaining the constants by parameterization on the basis of reference values of a substance. The reference values can includexe2x80x94as a function of the at least one characteristic to be ascertained by the improved apparatusxe2x80x94at least one of the density/mass, moisture content and dielectric constant of the substance to be tested.
The means for supplying microwave signals can also comprise means for substantially sinusoidally modulating the frequencies of the microwave signals with a relatively low frequency. Bands of modulated frequencies can include a basic frequency at a downwardly sloping flank of the resonance curve, particularly or preferably at an inversion point of such curve.
The resonator arrangement can comprise a preferably metallic housing having an inlet and an outlet for a flow of a substance to be tested (e.g., a tobacco stream). The housing can be dynamically balanced; for example, such dynamically balanced housing can include or constitute a cylinder. The resonator arrangement can further comprise at least one dielectric resonator in the housing, and such resonator can provide a path for the advancement of a substance (e.g., a cigarette rod) between the inlet and the outlet of the housing. The resonator arrangement can further comprise a tubular guide for the substance, and such guide can include portions at the inlet and at the outlet of the housing. A presently preferred guide extends through the at least one dielectric resonator. The just described resonator arrangement can further comprise conductive sleeves which surround the guide in the regions of the inlet and the outlet of the housing; such sleeves can contain or they can consist of a metallic material.
Alternatively, the resonator arrangement of the improved apparatus can comprise two resonators each of which receives microwave signals from the supplying means, one of which transmits the aforementioned high-frequency signals, and the other of which transmits to the evaluating means additional signals which are influenced by a reference substance to compensate for disturbances. Such resonator arrangement can further comprise at least substantially identical housings for the two resonators.
The at least one characteristic which is to be ascertained by the improved apparatus can be the density/mass of tobacco or the moisture content of cut tobacco in a cigarette rod or the dielectric constant of cut tobacco, particularly in a cigarette rod.
A further feature of the invention resides in the provision of a method of ascertaining at least one characteristic of a substance by means of a high-frequency resonator arrangement which is detuned in the presence of the substance to be tested. This method comprises the steps of supplying to an input of the resonator arrangement microwaves having two frequencies whereby an output of the resonator arrangement respectively furnishes first and second curves of high-frequency output signals in the presence and absence of a substance (the curves have amplitudes and sloping flanks and each of the two frequencies is allocated to a sloping flank of a curve), and evaluating the output signals including comparing the curves to ascertain shifts of resonance frequencies of the output signals due to the presence of a substance, and comparing the amplitudes of the curves to ascertain damping of output signals due to the presence of a substance. The just outlined method can further comprise the step of periodically varying the frequencies of the microwaves which are supplied to the input of the resonator arrangement, and the varying step of such method can include repeatedly switching between higher and lower frequency values.
Still further, the just outlined method can comprise the step of modulating the frequencies of the microwaves with a lower-frequency rectangular a-c voltage. The output signals can constitute d-c signals and the method can further comprise the steps of ascertaining those d-c signals which are transmitted by the output of the resonator arrangement at the minimum and maximum values of the modulated frequencies, and processing the thus ascertained maximal and minimal signals into evaluation signals. The processing step can include providing a further signal which denotes the sum of the maximal and minimal signals and processing the further signal into a signal denoting an average value of the maximal and minimal signals. Such processing step can further include providing an additional signal which denotes the difference between the maximal and minimal signals, transmitting the further and additional signals to discrete calculating stages, polynomially computing the maximal and minimal signals in the respective stages with constants to thus generate partial signals, and adding (summing up) the partial signals. Such method can further comprise the step of ascertaining the aforementioned constants by parameterization on the basis of those reference values of the substance which are to be ascertained. Such reference values can include the density/mass, the moisture content and the dielectric constant of the substance to be tested.
The substance to be tested can be tobacco, and the at least one characteristic can be the mass/density of tobacco. For example, the substance can constitute a rod-like filler of cut tobacco. Alternatively, the at least one characteristic can be the moisture content of tobacco, for example, the moisture content of successive increments of a rod-like filler of cut tobacco.
Still another feature of the invention resides in the provision of an apparatus for ascertaining at least one characteristic of a substance. The apparatus comprises a resonator arrangement, means for supplying to an input of the resonator arrangement microwave signals at two frequencies (the resonator arrangement has output means for the transmission of first and second high frequency signals which are respectively generated in the presence and in the absence of a substance at the resonator arrangement), and means for evaluating the first high-frequency signals. The evaluating means comprises means for comparing first and second resonance curves having amplitudes and sloping flanks. Each of the frequencies is allocated to a sloping flank of a curve and the first and second curves respectively denote the first and second high-frequency curves to thus ascertain shifts of resonance frequencies attributable to the presence of a substance at the resonator arrangement. The evaluating means further comprises means for comparing the amplitudes of the first and second resonance curves to thus ascertain the damping of such amplitudes by a substance.
The supplying means of the just discussed apparatus can comprise a microwave generator which is connected to the input, and a frequency regulator which is connected with the generator to periodically vary the frequency of signals from the generator between higher and lower values.
The apparatus can further comprise means for modulating the frequencies of the microwaves with a lower-frequency rectangular a-c voltage. The first and second high-frequency signals can constitute d-c signals, and the modulated frequencies have maximum and minimum values. The apparatus can further comprise means for ascertaining the d-c signals which are transmitted by the output means of the resonator arrangement at the minimum and maximum values of the modulated frequencies, and means for evaluating the ascertained signals into evaluation signals. The evaluating means can comprise summing and subtracting circuits having outputs for signals which are transmitted to discrete calculating stages having means for polynomially computing signals from the respective (summing, subtracting) circuits with constants to thus generate partial signals. Such evaluating means can further comprise means for adding (totalizing) the partial signals as well as means for ascertaining the aforementioned constants by parameterization on the basis of reference values of a substance. The reference values can include (as a function of the at least one characteristic to be ascertained) at least one of density/mass, moisture content and dielectric constant of the substance.
The resonator arrangement can comprise a metallic housing having an inlet and an outlet for the flow of a substance to be tested, such as a tobacco stream. The housing is or can be dynamically balanced and can include a cylinder. The resonator arrangement can comprise at least one dielectric resonator in the housing.
In accordance with one presently preferred embodiment, the at least one characteristic is the density/mass of tobacco and/or the moisture content of cut tobacco in a cigarette rod.
The novel features which are considered as characteristic of the invention are set forth in particular in the appended claims. The improved apparatus itself, however, both as to its construction and the mode of assembling, installing and utilizing the same, together with numerous additional important features and advantages thereof, will be best understood upon perusal of the following detailed description of certain presently preferred specific embodiments with reference to the accompanying drawings.